Fig. S1. Gata3 is not expressed before primitive streak formation. In situ hybridisation for Gata3 at pre-streak stages
X (A) and XIII (B) show no expression, whereas embryos at stage 5- (C) show expression in the prospective epidermis, as
previously reported (Sheng and Stern, 1999).
Fig. S2. GATA knockdown does not induce or extend Koller’s sickle. To test whether GATA knockdown could either
induce an ectopic Koller’s sickle, or somehow attract sickle cells, Gata2/3 morpholinos were electroporated anteriorly
(anti-fluorescein, brown) and embryos examined for ectopic expression of Chordin, which at this stage is specific for the
sickle (purple). Neither ectopic expression nor an extension of the endogenous domain into the electroporated region was
seen. The embryo shown is at stage XIII.
Fig. S3. Epistasis experiments to test whether GATA acts through induction of Vg1or Bmp4. (A,B) GATA-MO was
electroporated into the anterior half of an embryo (experimental design as in Fig. 4D), and expression of Vg1 examined
after 9 hours. An example is shown after in situ hybridisation for Vg1 (A) and the same case after staining with antifluorescein to reveal the morpholino-electroporated cells (B). In this case, Vg1 is upregulated in the region where GATA
was knocked down. (C-F) GATA-MO (C,D) or control-MO (E,F) was electroporated anteriorly in an intact embryo and
Bmp4 expression examined 6 hours later. GATA-MO causes slight downregulation of Bmp4 expression (C,D) when
compared with the control (E,F).